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Full text of "Cement dispersion and air entrainment in concrete pavement construction."

/304-/4 



RESEARCH PAPER NUMBER THIRTY-NINE 



CEMENT DISPERSION AND 

AIR ENTRAINMENT IN 

CONCRETE PAVEMENT CONSTRUCTION 



I 



<** *a 



*4? 



BY 

EDW. W. SCRIPTURE JR., PH.D. 

I > I R E C 1 O R 

Master Builders Research Labor Uo»*i^s 
CLEVELAND, OHIO 






Copyright 1942 - The Master Builders Company 



_. 



FOREWORD 



CONSTRUCTION of highways and other pave- 
ments presents a peculiar and difficult problem. 
The conditions to which such structures are 
exposed are particularly severe and properties not of 
primary importance in other work are required. 

During the last ten years cement dispersion has 
proved its value and economy in concrete construction 
generally. More recently the value of incorporating 
added air in concrete, particularly with reference to 
decreased scaling and added resistance to freezing and 
thawing has been recognized. 

A product combining these two principles has now 
been developed which combines the virtues of both. 
This paper has been written with the objective of 
acquainting highway engineers and others who would 
be interested with the nature of this product, the 
manner in which it functions, and the results which 
can be secured. 



ABSTRACT 

Highway concrete differs in its require romconci - lerally 

in certain respects. High transverse rod surfaces resistant 

to wear and scaling are particularly neo 

The incorporation of more than the normal amount of e 
air in the mix contributes to greater workability 
increased resistance to scaling, and improved dura 
entrainment may be secured by use of a portlan<- cement 

blend, a Vinsol resin cement, or the addition of a foaiv 
certain advantages and disadvanta- 
ge value of cement sion in concrete mixes has been es 
1 over a period o - effective in improving the prope 
of the concrete in both the md hare ( 

A material. HP-7. designed especially for highway or othe 
ment construction h: developed by combining the mc 

factory foaming agent with the most practical cement dis 
agent. The advantages of both are realized and 
a foaming agent are overcome. 

HP-7 is an effective me: s .ring those properties which 

have been sought from the use of portland-natural cement blends, from 
A insol res fcs, and from certain admixtures. It is, however, 

free from the disadvantages which these have. HP-7 may be 
effectively with any type of cement or blend. 

HP-7 appears to offer at least a partial solution and the most 
satisfactory solution so far available to the problem of securing high 
igth, prevention of scaling, increased durability, and improved 
wear res s in pavement construction. 



RELATION OF DISPERSION TO SPECIAI/CEMENTS 



Table of Contents 

Paire 
Introduction . 6 

Methods of Incorporating Air 7 

Natural Cement Blends 8 

Vinsol Resin Cements 9 

Foaming Agents 10 

( lement Dispersion 12 

Dispersing Agents, Foaming Agents, and Protective Colloids . 13 

Development of HP-7 15 

Effects of HP-7 16 

Kconomics of HP-7 13 

Relation of HP-7 to Special Cements . 19 

Relation of HP-7 to Admixtures 21 

Summary 22 

Test Procedure 23 



[5] 



CEMENT DISPERSION AND AIR ENTRAINMENT 
IN CONCRETE PAVEMENT CONSTRUCTION 

INTRODUCTION 

THE problem of concrete for highways presents some differences 
from that of concrete for general structural purposes. Highways 
are essentially large flat slabs of comparatively small thickness 
which are exposed to rather severe conditions. They must be able to 
carry heavy loads, to stand exposure to severe weathering conditions, 
and must have a wear resistant surface. These are conditions not 
usually encountered simultaneously in ordinary construction. 

The requirements of highway concrete are relatively high trans- 
verse strength to carry the loads, durability to resist attack due to 
exterior exposure and such added adverse conditions as de-icing with 
calcium chloride or salt, and avoidance of any phenomena which 
might impair the strength or durability of the surface. While it is 
usually possible to secure a satisfactory quality with respect to any 
one property of concrete, it is often difficult to secure a combination 
of properties which will be all that is desired. It is perhaps for this 
reason that a great deal of investigation has been directed to high- 
way concrete without as yet reaching any agreement on a wholly sat- 
isfactory solution. 

Two other properties of concrete are of some importance in high- 
way work. Workability in this type of concrete is essential, as it is 
in any other. There is usually little difficulty in securing adequate 
workability with the mixes commonly used. Volume change is also a 
factor in that, if excessive, undue cracking of the slab will occur. Ade- 
quate reinforcing and proper location of joints will usually prevent 
excessive cracking if a mix of any reasonable volume change is used. 

To secure high strength, compressive or transverse, is not in itself 
difficult. A mix of adequate cement content with a low water-cement 
ratio will be required. Further, any influence which tends to interfere 
with the hydration reactions or to impair the qualitv of the cement 
paste structure will be undesirable. 

Durability of the concrete as a whole is also not a serious problem. 
A low water cement ratio is required but without undulv high cement 
content.* High strength and low permeability will contribute to dura- 
bility. Recently there has been considerable work on the introduc- 
tion of small amounts of air into concrete bv various means. It ap- 
pears to be fairly generally believed that a small increase in entrained 
air adds substantially to durability. It seems probable that excessive 
air entrainment is undesirable as the beneficial effects would be over- 
come by the loss in strength. 

To secure a satisfactory surface is a more difficult problem and 
probably more important. In the first place the surface must have 
1 Lewis H. Tuthill. J. A. C.I. June. 1939, page 589. 

[6] 



. 



high strength to resist abrasion, in the second, high durability to with- 
si and the weather and treatments applied to the surface. F. H. 
Ja< kson ! of the Public Roads Administration, has summed up the 
situation as follows: 

"While a good deal of publicity has been given the matter of 
scaling in New York State, I personally have seen considerable 
scaling on concrete pavements in many other northern states. 
The scaling is, I think, undoubtedly associated with freezing 
and thawing and is, I believe, primarily the result of water gain 
or segregation during placing. This results in the formation of 
a thin porous layer on the top of the pavement which is an easy 
prey to the action of ice and salts used for ice removal. It is 
my opinion that the principal effect of the natural cement is to 
reduce the amount of this water gain, thereby producing a more 
uniform mix from bottom to top of the slab, and consequently 
a denser surface. I do not think there is anything very mys- 
terious about it. Furthermore, there may be other materials 
thai will accomplish the same thing/' 

METHODS OF INCORPORATING AIR 

A number of means have been investigated recently, both in the 
laboratory and by laying experimental roads for the entrainment of 
air to improve the quality of the highway by reducing bleeding. These 
include the use of blended cements, particularly portland-natural 
blends, the use of cements ground with various grinding aids such as 
rosin, beef tallow, stearates, and especially Vinsol resin, and the ad- 
Hi to the mix of foaming agents, especially Orvus (sodium lauryl 
sulphate). Each of these methods has its advantages and disad- 
i antages. 

All the foregoing methods of incorporating additional air into the 
mix have some effects in common. All necessarily lower the unit 
weight of the concrete. All reduce bleeding markedly and produce a 
more fatty or cohesive mix. 

It seems immaterial whether the unit weight of the concrete is 
increased or decreased as long as this is not an index of other prop- 

es. In the case of the air-entraining methods decreased wei 
up to a certain point, is a criterion of improved durabil 
Reduction in bleeding can hardly be anything but beneficial. It might 
be thought that increased cohesiveness or fattiness as an aspen 
workability would be beneficial, but, with the methods of finishing 
commonly used in highway work such does not appear to be the case. 
The fattier mixes tend to pull and are more difficult to finish. To 
secure reduced bleeding, however, it seems to be necessary to increase 
cohesiveness. 

The effects of air entrainment on bleeding are discussed by Powers* 
as follows: — 

"Some materials, when added to a mix or when ground with the 
cement, cause the formation of a comparatively stable foam which 
gives the mix a high air content. This has a pronounced effect on the 
rate of bleeding through a reduction in the effective capillary area 

** A.S.T.M. Proc, Vol. 38, 1938 — Discussion, page 352. 

*The Bleeding of Portland Cement Paste, Mortar and Concrete — by T. C. Powers, 
Research Laboratory of the Portland Cement Association — Bulletin 2. 

[7] 



per unit gross cross-sectional area and through the effect of the buoyancy 
of the bubbles on the force causing bleeding. The effect of the air 
can be established by treating it as if it were an aggregate added to 
the paste, an aggregate having definite volume but negative weight. 

"It will be observed that the entrained air effects very substan- 
tial reductions in the bleeding rate and that the calculated values are 
in good agreement with the observed except in the case of the highest 
air content. This latter value was checked and the discrepancy found 
not to be due to error. It is believed that, when the air content be- 
comes sufficiently high, the bubbles, ceasing to act independently, tend 
to merge their boundary films and knit the whole mass together by 
means of surface tension forces. With this amount of air the paste 
will 'stand up' like whipped cream. It is possible also that the effect 
of added surface in reducing the hydraulic radius may be involved, 
but this seems doubtful, for examination under the microscope indi- 
cated that the bubbles were large enough to have a low specific sur- 
face. It was for this reason that the surface effect was neglected in 
developing the above equations. 

'These tests on neat cement paste do not tell the whole story of 
the effect of air on bleeding as it would be experienced in practice, 
for in these tests the water-cement ratio was constant. In practice, 
the use of a foaming agent in a given mix permits a substantial reduc- 
tion in the water-cement ratio because of the fluidity of the air itself. 
The effect of such a reduction in water, superimposed on the effects 
expressed by equation 36, would result in a very low bleeding rate 
as compared with that of the same mix made without the foaming 
agent. It seems therefore that this method of reducing bleeding de- 

es further study, especially in view of the recent tests which indi- 
on of a high proportion of air by means of a 
ases the resistance to frost action." 

Each of the air entrainment methods is considered individually 

Natural Cement Blends 

Natural cements were produced prior to the development of port- 

5. In the early days Portland cement was used as an 
i natural cement concrete to improve the strength, espe- 
The natural cements, as the name implies, are 
produced from a naturally occurring "cement rock" which has a com- 
position similar to that of the Portland cement raw mix. The cemen- 
! i T !" of the "rock" are developed by burning to tempera- 

fiat lower than the for production of port land 

In certain respects natural cements are superior to normal port- 
land cement, although they vary widely anions themselves. Because 

natural cement imparts desirable properties to the concn 
not necessarily imply that some other natural cement will do 
wise. The advantageous properties of natural cements are a gre 
degn r "fattiness" which reduces bleeding and seg- 

regation, greater durability, and lower heat evolution 
advantages are slower rates of setting and hardening, lower B1 
at least until after very long curing, and a higher water • tnent 

for a given i r cy. 



1 here is no >nt on the causes tor the properties of natural 

cements. It may be that the natural origin of the "cement ro 
the lower burning temperature produce 

er watei and hence fatl 

hand, the properties of these cemei 

linment of a higher proportion of air in the mix which h 
in turn, ascribed to small amoui 
purposeh included in the 1 1 

• rved increases in durability mighl • • 
reduced bleeding, which would help 

: entrained uir More p 
sible. The lower heal evolution, a 
development , are 6b\ ion 

Vinsoi Resin Cements 

A number of materials I 
reduce ih»* amount of grindii ent clinker to pi 

of the required finen< 
more or less effective are \ insol resin, i 

and Others. In addition to i he function 

tatinjj grinding, i hej also affect th< vhen 

- in concrete wil h respect part i u 

md t h«- i 



The best known grinding rid oi 
used to a certain extent is \ h 

\\ hen porl land < i 
mall amount of V insol i 

I lj facilitated. \\ hat is more 
Burner, a cement 

of air and to be more cohesh e or fat ■ . In r 
>und cements produ< • the 

Of natural with Portland 



which I 

t clii • 

ommonl 
impor 











TABLE 


1 








Vlnsol Resin 


Ground Cement 












C 


oncrete 


Mix 


nenl 


















Sand 




































s 'th 






















( foment 


















A 


None 


2090 


7 6 












A 




2125 


7 1 




M 








B 


None 


1920 


7 2 












B 




1982 














C 


None 


1665 


7 




•J7 • 






151 


c 




1650 


6 B 




20* 






1 15 5 


I) 


Mone 


2100 


7 5 




flQ 








I) 


03< , 


2090 


7 \ 




241 









The \ 'insol cement suffers from tl 
port land-natural blend in th 
strength appears to be greater for the Vinsoi res 



the blend and. moreover, it is permanent: that is. with long curing 
the strength of the concrete made with a portland-natural blend will 
probablv equal that of a straight portland mix. whereas the \ insol 
resin cement will always show lower than normal strengths. Appar- 
ently the loss in strength is directly related to the amount of air en- 
trained. Some strength data on cement ground with and without 

3 .1 resin are given in Table Xo. 1. It is especially to be noted that, 
although the water-cement ratio is lower for the Yinsol resin cement. 
due to the replacement of water by entrained air. the strengths are 
markedly lower instead of higher as would be expected. 

Another difficulty with Yinsol resin cements is that their behavior 

tv variable. The effect of a given percentage of Yinsol resin, as 
measured for example by the decrease in unit weight of the concrete 
which is an index of the* amount of air entrained, seems to vary with 
different cement clinkers: even with clinker from the same mill pro- 
duced at differer. ^nation implies that the effective 
of the Yinsol resin with respect to air entrainment. bleeding, segre- 
gation, fattiness, durability, and strength will van'. In the present 

e of our knowledge these variations are unpredictable. This means 
that, because a certain percentage of Yinsol resin is ground with the 
cement clinker, it does not : ily follow that the desired prop- 

erties will be secured. A better criterion of the effectiveness of a 
Yinsol resin cement would seem to be the drop in unit weight of con- 
crete made with the cement in question compared with a similar mix 
from normal portland cemer. seems to be a matter 

of trial and error from one lot of cement to another. 

\ 'insol resin cements have been offered and to some extent used 
as a substitute for portland-natural cement blend, to produce similar 
properties in the concrete mix, particularly increased fattiness and 
Tendency towards scaling. They are competitive on a cost basis, 
as neither adds substantially to the cost of the concrete. Considering 
the variability of the Yinsol resin cement and the losses in strength 
which may result it would seem that, if the quality of workability 
:i either Yinsol resin cement or the portland-natural blend will 
impart is desired, the choice would be on the latter. 

Rosin, beef tallow, oil. and similar materials are very similar to 
Yinsol resin. Lik< they also impair strength. On the whole, 

such informatio: available would indicate that they are less 

satisfactory than Yinsol resin and there is no evidence that they have 
received any general acceptance although some experimental high- 

v installations have been made. 

Foaming Agents 

A large number of organic compounds will produce foaming. They 
decrease the surface tension of water and those which are highly effec- 
tive in this respect are also known as wetting agents. Any material 
• ill produce a stable foam will, when addecl to a concrete mix. 
tend to increase the amount of air entrained. 

s -sion x of the general nature of wetting agents and their 
behavior is as follows: — 

'"In general, wetting agents are more or less complicated chemical 
molecules composed of two essential parts. One is termed 'hydro- 

Trom A .meriean Cyanamid & Chemical Corp. 

[10 1 



philic, and it is the portion which draws the agent into water or is 
attracted to surfaces which are the more polar. The other part of the 
molecule is termed 'hydrophobic/ and it tends to leave the water and 
attach itself to or dissolve in an oil or other non-polar medium Such 
a molecule will orient or align itself at the interface, so that the hydro- 
phihc part will be in the water and the hydrophobic part in the or- 
ganic phase. t The fundamental governing factor in such orientation 
is the attraction of like atoms or groups of atoms for one another. 

"Wetting agents belong to a group of a more general class of mate- 
rials called 'surface active agents,' and among their properties is their 
ability to lower surface tension and interfacial tension. Surface ten- 
sion values of solutions of a wetting agent are a measure of the effec- 
tive amount of the material collected at the air-solution interface; 
whereas interfacial tension values are a measure of the amount of 
material collected at the liquid-liquid interface and consequently are 
a measure of its surface activity. 

"Surface activity is a special property and will vary from inter- 
lace to interface. That is to say, because a wetting agent may be help- 
ful in causing water to wet a hydrophobic material, it does not neces- 
sarily follow that it will be effective in promoting better wetting of 
a hydrophihc surface. Since conditions at the liquid-liquid interface 
more nearly approximate the conditions under which wetting agents 
are used, it is a fact that interfacial tension values are a more exact 
indication of wetting action than are surface tension values. 

"The degree of surface activity of such an agent depends primarily 
upon the ratio of its hydrophilic to its hydrophobic constituents. This 
ratio or 'balance' is markedly affected by the nature of these antago- 
nistic groups and by their relative position in the molecule. Advan- 
tage is taken of the factors influencing balance to formulate products 
suitable for specific purposes. The presence, concentration, and chemi- 
cal nature of other ingredients in the system determine to a large ex- 
tent the final hydrophilic-hydrophobic balance of the agent." 

With respect to decreased unit weight, decreased bleeding, and in- 
creased durability, the effects of a foaming agent are essentially the 
same as those of a portland-natural blend, or of a Vinsol resin cement. 

With respect to the other properties of the concrete, foaming 
agents vary widely. Many of them seem to interfere with the hydra- 
tion reactions of the cement, thereby decreasing strength and possibly 
increasing permeability. It is possible, however, to select a foaming 
agent which does not impair the normal reactions of the cement and 
of these Orvus appears to be the most suitable. 

By addition of Orvus to the concrete mix the same effects with 
respect to unit weight, bleeding and durability can be secured as with 
a portland-natural blend. Unlike the latter, strengths are not im- 
paired and instead of increased water-cement ratio for a given con- 
sistency the required water is appreciably reduced. Further, lauryl 
sodium sulphate is a definite compound so that its properties remain 
constant as is not true of different brands of natural cement and pos- 
sibly even of different lots of natural cement from the same source. 

As compared with a Vinsol resin cement, addition of Orvus to the 
mix will have similar effects with respect to reduction of unit weight, 
bleeding and water requirement, and increased durability and cohe- 
siveness. Unlike the Vinsol resin cement, it does not impair the 



[11] 






strength but should show some increase at all ages. Again, being a 
definite compound, it is not subject to the variability of Vinsol resin 
cements. 

CEMENT DISPERSION 

The principle of cement dispersion has been fully discussed in 
Research Papers Xos. 35 and 36, but a brief review of this subject is 
included here. 

When portland cement is mixed with water, the individual par- 
ticles tend to gather together and stick to each other in clumps, i.e., 
the solid-liquid system is flocculated. This is due to lack of mutually 
repellent electrostatic charges on the cement particles. If a suitable 
dispersing agent is introduced into the mix, the clumps are broken 
up and the cement then acts as individual particles, i.e., is dispersed. 

Dispersion of the cement produces two important effects. The 
water which had been trapped within the particle clumps is released 
to become a part of the mixing or placing water. The surface area of 
the cement in contact with water is greatly increased, since the par- 
ticles are no longer in contact with each other. As a result of the 
first the amount of water required in the mix for a given consistency 
is less, i.e., the water-cement ratio is reduced. Since the value of the 
cement is dependent on a hydration reaction which is a surface phe- 
nomenon, the second effect which promotes more rapid and more 
complete hydration permits more efficient utilization of the cement. 
By the reduction in water-cement ratio and by the increase in sur- 
face area of cement available for hydration, the potential value of the 
cement is more completely realized. 

Those properties of concrete which are dependent on the surface 
area of the cement and on water-cement ratio, and this includes most 
of them, must necessarily be improved by dispersion. These effects 
are realized in the concrete in both its plastic stage and subsequent 
to hardening. 

During the plastic stage, dispersion of the cement in a given mix 
will produce more placeable concrete with less water, due to the re- 
lease of water from the cement clumps. The fattiness of the mix is 
increased, wiiile segregation and bleeding are reduced, due largely to 
the increased effective surface area of the cement. Volume change 
before hardening is markedly decreased, due in part to the lower water 
content and in part to the greater surface area. 

A greater uniformity and freedom from gross defects of the hard- 
ened concrete may be expected from the improved properties in the 
plastic stage. Greater watertightness with reduced permeability and 
absorption are realized through the lower water content required for 
placing. Higher strengths and greatly increased durability with re- 
spect to both freezing and thawing and sulphate corrosion may be 
attributed to the lower water-cement ratio of the dispersed mix' and 
to the increased surface area available for hydration. 

Although dispersion of the cement will accomplish most of the 
effects of foaming agents and portland-natural blends or Vinsol resin 
cements including decreased bleeding, increased durability, and in- 
creased cohesiveness, it attains these results by an entirely different 

[12] 



means. Furthermore, it produces these effects without the disad- 
vantageous properties of those methods which entrain large amounts 
of air but with other advantageous properties of its own. 

Cement dispersion does not produce its effects by the incorpora- 
tion of large amounts of air but by reduction of water-cement ratio 
and by making available for hydration or water retention a larger 
surface area of the cement. By using a cement dispersing agent, the 
unit weight of the concrete is not reduced appreciably (depending on 
the type of mix and method of handling a dispersed cement mix will 
show slightly higher or slightly lower unit weight than a comparable 
undispersed cement mix). Since dispersion permits a reduction in 
water for a given consistency, this means that in most cases there 
will be somewhat higher air entrainment with the dispersed cement 
but this is not large and is not of a magnitude comparable to the 
effect secured with a foaming agent. 

DISPERSING AGENTS, FOAMING AGENTS and 
PROTECTIVE COLLOIDS 

At this point it may be well to point out the very definite differ- 
ences between dispersing agents, foaming or wetting agents, and pro- 
tective colloids. They might be considered in relation to any solid- 
liquid system, but for present purposes the discussion may be con- 
fined to water as the liquid since cement is a typical solid-water system 
in which the solid reacts with the liquid. 

A dispersing agent is a compound which, presumably by adsorp- 
tion in an oriented manner, causes the particles of the solid in suspen- 
sion in the liquid to become mutually repellent, presumably because 
they are thereby endowed with like electrostatic charges at the sur- 

e. Dispersing agents are specific: that is, a compound which is a 
dispersing agent for one solid-liquid system may or may not be a dis- 
persing agent for some other system. Dispersing agents may or may 
not lower or raise surface tension. They may or may not cause foam- 
ing. The most satisfactory dispersing agent for cement in water has 
a small but not marked effect in decreasing surface tension and does not 
cause formation of stable foams. Dispersing agents, used in the pro- 
portions suitable for dispersing cement in water, do not interfere with 
the hydration reactions of the cement. 

Foaming or wetting agents greatly lower the surface tension of 
water. They form stable foams. They are not dispersing agents for 
cement in water. Used in moderate quantities to produce air en- 
trainment, at least some of them do not interfere with the hydration 
reactions of the cement; others probably do. One case is known of 
a foaming agent which is also a cement dispersing agent, but this 
would seem to be a fortuitous combination as there is no necessary 
relation between these two actions. 

The difference between the action of a cement dispersing agent 
and a foaming or wetting agent in water is illustrated in Fig. I. 

Protective colloids will stabilize a suspension of a solid in a liquid, 
that is, the protective colloid will be adsorbed on the solid particles, 
preventing these from coming in close contact and hence preventing 
to some extent coalescence. A protective colloid will stabilize a solid- 
liquid system in which the solid is already dispersed by a dispersing 
agent or other means. In a flocculated system the protective colloid 



13] 






Fig. I 



° 



"*- In tube containing the 
foaming agent, note form- 
ation of a stable foam, 

~ is absent in 
containing the dispersing 
agi. > 

In this manner the foaming 
agent introduces a large 
quantity of air into the mix. 

















will stabilize the system in the flocculated condition. Protective col- 
loids do not have any large effect on surface tension and are not gen- 
erally dispersing agents. Therefore, a protective colloid added to a 
cement-water system does not produce dispersion. Some particular 
protective colloid may also be a cement dispersing agent but this is 
rare and is perhaps better stated that some dispersing agents for ce- 
ment may also be protective colloids. Protective colloids are not in 
themselves active foaming agents but they do tend to stabilize foams. 
The adsorption of a layer of protective colloid on the surface of the 
cement particles appears to interfere with hydration. 

A suspension of cement in water may be termed a rather gross 
colloidal system. Only a small portion of the cement particles of 
smallest size are really of colloidal dimensions and will stay suspended 
indefinitely. The effects of dispersing agents, wetting agents, and pro- 
tective colloids are therefore less marked and less clear cut than they 
would be in a truly colloidal system. This is a matter of degree rather 
than of the nature of the phenomena. The finer the cement is ground 
the more closely its behavior will resemble that of a true colloidal 
system and for this reason the effects of a dispersing agent are more 
marked with a fine cement. 

It is also true that as commonly used in a concrete or mortar mix 
the cement and water are in such proportions that they form a paste 
rather than the dilute suspensions usually employed for the study of 
colloidal phenomena. The solid particles no longer move as freely 
in the liquid medium. There is, however, no doubt that^ the same 
phenomena occur, although they may manifest themselves in a some- 
what different manner. For example, dispersion has a, marked effect 
in lowering the viscosity of a suspension of a solid in water having 
in the flocculated condition a viscosity appreciably higher than that 

vater. As the suspension becomes more dilute and in any condi- 
tion, flocculated or dispersed, approaches the viscosity of water, this 
effect becomes less marked and as the suspension becomes more con- 
centrated and higher in viscosity it becomes more pronounced. These 
are well known effects which have been observed in clay and other 
suspensions and put to practical application in casting with clay slips 
and in similar processes. In such solid-liquid systems the relation be- 
tween dispersion, viscosity and adsorption can be followed through 
alternate cycles of flocculation and dispersion. Similar phenomena are 
exhibited by suspensions of cement in water of paste consistent. 

DEVELOPMENT OF HP-7 

The benefits to concrete of cement dispersion have been estab- 
lished in this and other laboratories and in the field during a develop- 
ment which has extended over more than ten years. The advantages 
derived through the application of this principle to the properties of 
concrete generally have been described elsewhere (Research Paper 
No. 35) as has also its economic value (Research Paper Xo. 36). These 
advantages are equally applicable to highway concrete generally, but 
there remained the possibility that, to fit the special requirements of 
highway work, other principles could be applied which would more 
nearly approach a solution of this special problem. 

[15] 



Within recent years the desirability of incorporating somewhat 
more air in concrete than is ordinarily entrained has been investigated 
in this and other laboratories. Now there appears to be little question 
that certain benefits are secured by this means as described above. 
Certain of the highway departments have pursued this subject some- 
what further as has also the Portland Cement Association and a num- 
ber of experimental roads have been laid using what may be called 
air incorporating agents. The most satisfactory such material seems 
to be Orvus (sodium lauryl sulphate) and at least one highway de- 
partment has definitely reported that observations from a compari- 
son of a number of experimental road sections have indicated that 
this is the case. 

The introduction of air into the cement paste is undoubtedly at- 
tended by undesirable effects, whether or not the benefits of so doing 
outweigh the disadvantages. It appeared that a combination of the 
principle of dispersion with that of air incorporation might solve these 
difficulties. By dispersion of the cement it should be possible to over- 
come the deleterious effects of air incorporation and to superimpose 
the benefits of cement dispersion. 

From these considerations HP-7 was developed. It is essentially 
a combination of the best air incorporating agent, sodium lauryl sul- 
phate, with the most satisfactory and economical cement dispersing 
agent, a derivative of lignin sulphonic acid. 

EFFECTS OF HP-7 

As would be expected from its composition, HP-7 produces two 
effects, that of a dispersing agent and that of a foaming agent. 

The effects of a dispersing agent on a concrete mix are those which 
have been described elsewhere. They are essentially as follows: — 

A. In the plastic state of the concrete: — 

1. More placeable concrete with less water 

2. Increased fattiness 

3. Reduced segregation and bleeding 

4. Greater water retentivity 

5. Reduced shrinkage before hardening 

B. In the hardened concrete:— 

1. Increased durability 

2. Increased watertightness 

3. Higher strength 

4. Lower volume change 

5. Lower permeability and absorption 

6. Greater uniformity and freedom from gross defects 

The effects of the introduction of additional air by means of a 
foaming agent are essentially as follows:— 

A. In the plastic state of the concrete: — 

1. Increased fattiness 

2. Reduced bleeding 

B. In the hardened concrete:— 

1. Increased durability 

2. Greater uniformity and freedom from gross defects. 

3. Strength unaffected by a suitable foaming agent but 

reduced by others. 

[16] 



With respect to fattiness and bleeding, the dispersing agent and 
the foaming agent reinforce each other. The same is true of dura- 
bility and uniformity of the concrete. The dispersing agent overcomes 
any tendency of the foaming agent to lower strengths by diluting the 
cement paste with air and actually produces increases in strength. 

As a consequence HP-7 attacks the problem of improving high- 
way concrete at those points which have, in the past, been the most 
vulnerable. The effect on durability and bleeding is illustrated by the 
results of freezing and thawing (with calcium chloride) tests shown in 
Fig. II. The effects on strength are shown in Table II. It is hardly 
possible to express fattiness or freedom from gross defects quanti- 
ely but there can be little doubt, as has been shown by numer- 
ous qualitative observations by many different observers, that HP-7 
does markedly improve these properties. 

Fig. II 
Effects of Freezing and Thawing (with calcium chloride) on the 
surfaces of slabs. The same concrete mix at the same slump was used 
in each case. 




Addition 

None 

HP-7 1# sk 

None 

HP-7 1 # sk 

None 

HP-7 1 # sk 

.••rete Mix- 



Plain With iir : 

TABLE II 
TEST RESULTS 

Compressive Strength 

Lbs. In. Lbs. per sq. in. per 

\\ ater Slump 3 days 7 days 28 days Sack 

21.56 2i. 1420 2140 3410 8.0 

18.44 3 1770 3090 4080 6.9 

21.31 2% 1560 2350 3290 8.0 

17.63 1840 2550 3670 6.6 

21 69 -V j 1310 2020 2940 8.15 

17.88 2y 2 1880 2850 3700 6.75 

- Cement (Portland I 30 lbs. 

Sand. 90 lbs. 

Stone V 133 lbs. 

[17] 



ECONOMICS OF HP-7 

The actual cost of the materials which compose the concrete mix 
used for highway concrete is undoubtedly only a very small portion 
of the total cost of highway construction. The cost of any material 
which had even a small influence in prolonging the life of the con- 
crete and which caused only a small percentage increase in the cost 
of these materials would be amply justified. The increase involved 
in adding HP-7 to an ordinary highway mix would amount to about 

i if the cost of the materials and this might be estimated as amount- 
ing to not more than 0.1^ of the total cost of the highway. If even 
increase in the life of the concrete were secured by this means, 
the expenditure would be well warranted. 

This is not, however, the situation. Life of the concrete is increased 
to a vastly greater extent and this increase can be secured at no 
additional cost. The cost of adding HP-7 to the average highway 
concrete mix amounts to about the equivalent of the addition of 
1 2 additional sack of cement. The greatly increased durability of a 
mix with HP-7, costing approximately the same as a similar mix 
without HP-7, is illustrated in Fig. III. 



Fig. Ill 
Effects of Freezing and Thawing (with calcium chloride) on the 
surfaces of slabs. The plain mix is at the same consistency as the mix 
with HP-7 but contains ] 2 sack additional cement per cubic yard. 




Plain 



With HP-7 



Y\ ith respect to the other properties of these two mixes, the strength 
is not decreased but increased Table III . Permeability and adsorp- 
tion are decreased. Volume change is reduced. Segregation, shrink- 
age before hardening, are decreased. Uniformity, watertightness, 

water retentivity, and placeability are increased. 

3 means essentially that, at a given cost, the quality of the 
concrete is improved by the incorporation of HP-7 and that as a con- 
tence a highway of longer life with greater freedom from scaling 
is secured at no additional expense. 



I 18] 



TABLE III 

Compressive Strength Gals, 
SERIES I Lbs. In. Lbs. per sq. in. per 

Addition Water Slump 3 days 7 days 28 days Sack 

Xone 21.56 2' > 1420 2140 3410 SO 

HP-7 l#/sk- 

10% less cement 18 . 31 2* , 1450 2460 3360 7 . 65 
SERIES II 
Addition 

Xone 21.31 2 ; , 1560 2350 3290 8.0 

HP-7 lr sk- 

10' ; less cement 17 . 38 2 , 1730 2520 3610 7 . 25 
SERIES IV 
Addition 

Xone 21.69 2'> 1310 2020 2940 8.15 

HP-7 1^ sk- 

10% less cement 17.56 2y 2 1730 2570 3560 7.35 
HP-7 l#/sk — 
13' < less cement 17.56 3 1290 2000 2970 7.65 

Concrete Mix - Cement (Portland) 30 lbs. 

Sand 90 lbs. 

Stone (%") ....133 lbs. 

Normal Portland Cement 
Plain HP-7 

Cement -- lbs 574 4!»!» 

Sand - lbs 1134 1123 

( travel - lbs 2099 2070 

Water - gals 31.2 28.2 

Slump - in V/i 2}i 

( Jompressive Strength — 
Lbs. per sq. in. 

delays 2630 2250 

7 days 2790 2910 

28 days 3430 3750 

RELATION OF HP-7 TO SPECIAL CEMENTS 

The only special cements which have been proposed for highway 
work are the portland-natural blends and cements ground with a 
grinding aid such as Vinsol resin. The effects of these have been de- 
scribed above. 

HP-7 will produce similar effects to those of portland-natural ce- 
ment blends and will further give results not obtained with these. 
With HP-7 the increased water-cement ratios of natural cement blends 
for a given consistency are not required but decreases are secured. 
The early strengths are not impaired but increased. The variability 
encountered with different natural cements is not encountered and a 
definite controlled result is produced. 

In addition the desirable properties which spring from a decreased 
water-cement ratio such as lower volume change, increased strength, 
and increased watertightness are realized. There would seem to be 
no question that, for a given result, the more desirable means of se- 
curing it, as compared with a portland-natural blend, would be the 
use of HP-7. 



[19] 



There is, however, another way of looking at this question. Natu- 
ral cement blends undoubtedly have beneficial effects on highway 
concrete which seem to outweigh their disadvantages. It may seem 
desirable to use such a blend. In this case HP-7 will have the same 
advantages in a portland-natural blend as it will have in a straight 
Portland cement mix. Strengths will be equal or greater (Table IV), 
bleeding will be further reduced and durability increased, (Fig. IV). 
Here also volume change will be decreased, watertightness and other 
properties improved. 

TABLE IV 



Cement — lbs. 

Sand - lbs. 
Gravel 
>er 

Slump in. 

Strengt h. 

Lbs .in. 

• • sq. in. 



plain 

< Concrete with HP-7 

Purl land Blend plain 

i qua! consistency slump . 



*lend Portland <s:}i,/, 


-Natural 16^% 


Plain 


HP-7 


562 


503 


1110 


113 


205(i 


2085 


32.9 


29.4 


IV 


l 7 v 


1970 


2075 


2310 


2750 


2760 


3320 


525 




556 


590 


Pig. [V 




Thawing with calcium 


chloride on 



^m^femn 






m 1 * 




1 






; 






J^l 


[ 1 










"^ . 


^ 






n H 



,i\ 









In comparison with Vinsol resin cements, the situation is much 
the same Fig. V . The same effects can be produced at the same 
or less cost. Further, other properties such as volume change, water- 
tightness, and so forth, are improved. The Vinsol resin and similar 
ally show losses in strength if they are effective in incor- 
porating air. If they are not effective in this respect they are useless. 
HP-, increases in strength, consequently, for a given strength, 

pressive or transverse, a concrete mix with HP-7 can be produced 
at definitely lower cost. It should not be overlooked that for highways 
transverse strength is an important factor in view of the loads which 

ways are required to carry. 

Fie. V 
Effects of Freezing ,and Thawing (with calcium chloride) on the 
aces of slabs. All mixes are of the same design and at the same 
All the cements are made from the same clinker and 
have equal surface area ( 1660 sq. cm. per g). 





; i .Mm v w * C, * 

■j 

1 \ 





AITH 
HP-7, COMPRESSIVE 

' H AT 28 DAYS, 
4^0 LBS. PER SQ. IX. 



Normal Portland 
Cement, compressive 
strength at 23 days, 

3210 lhs. per sq. in. 



D WITH .032 

Vinsol Resin, compres- 
sive STRENGTH AT 28 DAYS, 
2660 LBS. PER SQ. IN. 



Airain, from the other point of view, HP-7 can be used in conjunc- 
tion with a Vinsol resin cement or similar cement to produce the de- 
sired properties in a higher degree and at lower cost. In this case, 
however, care should be taken to design the mix in such manner that 
an excess of air is not introduced. 

RELATION OF HP-7 TO ADMIXTURES 

The part played by admixtures has been discussed at some length 
in Research Paper Xo. 38. As far as highway construction is con- 
cerned the only admixtures which might be of interest are those foam- 
tgents which incorporate additional air. 

In some cases high early strength is a factor so that calcium 
blonde might be considered as also high early strength ce- 
ment and additional cement. These topics in their relation to 
ement dispersion are discussed in Research Paper Nos. 36 
:7and38.) 



[21] 



The foaming agents undoubtedly offer some advantages with re- 
spect to air inclusion as it improves durability and reduces bleeding. 
This has been discussed above. HP-7 includes a suitable proportion 
of the most satisfactory foaming agent. In addition it applies the 
principle of cement dispersion to highway concrete, thereby over- 
coming the disadvantages of foaming agents alone and adding the 
benefits of cement dispersion. 



SUMMARY 

HP-7 is a combination of those two principles which seem to offer 
the greatest chance of solving the problem of durable wear resistant 
highways. The employment of a foamine agent causes increased air 
incorporation and thereby increases fattiness, durability, and resist- 
ance to scaling and decreases bleeding. The application of cement dis- 
persion offsets the disadvantages of a foaming agent such as diminished 
strength, increased volume change and possibly increased water-cement 
ratio. It further yields the advantages to be derived from reduced water- 
cement ratio and more effective use of the cement by making an in- 
creased surface area available for hydration. 

Economically, the use of HP-7, by designing the concrete mix 
with this material, permits all the advantages of cement dispersion 
and air incorporation to be secured at no additional cost. 

In comparison with certain special cements such as natural- 
portland blends, or grinding-aid (Vinsol resin > cements, the same ad- 
vantages may be secured at lower cost without the disadvantages of 
these "cements. With these special cements themselves, HP-7 secures 
not only the benefits of the special cements but adds to them.* 

Admixtures in general do not produce the results of HP-7. Foam- 
ing agents offer some of its advantages but have also some undesir- 
able effects. Since HP-7 combines the best of the foaming agents with 
cement dispersion, it produces results which cannot be secured with 
admixtures generally and moreover at substantially lower costs. 



• With these special cements it is possible that a cement dispersing agent 
without foaming agent could be used to greater advantage than HP-7. 

[22] 



TEST PROCEDURE 

In order to determine the real value of HP-7 it is necessary to 
carry out a testing program to show its effects on the properties of 
the concrete and its economic value. For this purpose the following 
program is suggested. 

First select the most satisfactory mix which it is possible to design 
from the materials available and using whatever cement seems most 
advantageous. Then proceed as follows:— 

A. Workability and Water Cement Ratio — 

With selected mix make mixes and determine slump (and flow 
if desired) with and without HP-7 at equal w c. 

B. Stn ngth — 

With selected mix make concrete mixes at equal slump (or flow) 
as follows: — 

1. Selected mix — plain 

2. Selected mix with HP-7 

3. Selected mix less 10% cement with HP-7. 

Make cylinders for compressive strength determinations at suit- 
able ages (7 and 28 days), making not less than three specimens 
for each age. Make beam specimens for transverse strength if 
desired. 

( . Durability — 

a Make block specimens from same mixes as under B, 10" x 10" 
by not less than 5". Cure for 28 days and subject to freezing 
and thawing with calcium chloride. For this purpose build 
dike around edges of specimens with caulking compound, 
putty or other suitable material. Cover with water and 
freeze, remove from freezing chamber and thaw with fixed 
amount of calcium chloride. Repeat this cycle until appre- 
ciable deterioration of surface on plain mix is observed. 

(b) Make cylinder or beam specimens from same mixes as under 
B. Cure 28 days. Subject to freezing and thawing in satu- 
rated condition. Determine deterioration at suitable inter- 
vals by loss in weight, expansion or sonic method. 

D. Water tightness — 

Make specimens from mixes as under B, cubes, blocks, cylinders, 
or cut specimens from test pieces made under B. After 28 days 
curing allow to dry out in air. Weigh. Immerse in water and 
determine weight at suitable time intervals until constant weight 
is reached. 

E. Wear Resistance — 

Make block specimens as in C-a from same mixes as given under 
B. Make these specimens with smooth trowel finish. Test for 
resistance to abrasion by any accepted method. (A good method 
for testing abrasion resistance rapidly is described in the Journal 
of the American Concrete Institute, Sept. -Oct., 1937, page 17.) 

[23] 




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